Molecular Dynamics Simulation of Structure and Thermodynamic Properties of Poly(dimethylsilamethylene) and Hydrocarbon Solubility Therein: Toward the Development of Novel Membrane Materials for Hydrocarbon Separation

Abstract

Molecular dynamics simulation is used to model the structure and thermodynamic properties of a novel rubbery polymer with promising membrane properties for hydrocarbon separation. A realistic united atom force field is developed based on extensive density functional theory quantum mechanics calculations for a model dimer and volumetric data at various temperatures and pressures. Both a constant bond length and a flexible bond length model are examined. Well-equilibrated structures of the polymer melt at various conditions are used to evaluate numerous thermodynamic properties, such as the isothermal compressibility, thermal expansion coefficient, and cohesive energy density, and structural properties, including intra-and intermolecular distribution functions and the static structure factor. The microscopic structure of the free volume of the polymer matrix and its evolution with time affects the diffusion of penetrant molecules considerably; they are calculated accurately using the Greenfield and Theodorou geometric analysis. The solubilities of various n-alkanes from methane to n-hexane at 300 and 400 K are calculated using the Widom test particle insertion technique. In all cases, simulation results are in good agreement with literature experimental data for the volumetric properties of the polymer melt and the solubility coefficients of n-alkanes in the polymer. In a forthcoming publication, the transport properties of these systems and the underlying molecular mechanisms will be examined.

Molecular Modeling Investigations of Sorption and Diffusion of Small Molecules in Glassy Polymers

“…A large number of test particle insertions are implemented in well equilibrated configurations of the polymer systems obtained from MD or MC simulations. The method has been widely applied for the estimation of low concentration sorption of small molecules in polymer systems [7,43,44,45].…”

Molecular modeling investigation of the fundamental structural parameters of polymers of intrinsic microporosity for the design of tailor-made ultra-permeable and highly selective gas separation membranes

“…This fractional free volume consists of many isolated spaces of variable volume and size, which can normally be determined experimentally by Positron annihilation lifetime spectroscopy (PALS). Detailed information on the particulars of the free volume can be provided by applying computational modeling and molecular dynamics simulations [2,7,13]. By manipulating the polymeric chains and the size, shape and distribution of the nanochannels, the free volume in the polymeric matrix can be tuned to provide variations in the membrane permeability and selectivity [14,15].…”

Molecular simulation of realistic membrane models of alkylated PEEK membranes

“…The prediction of transport properties of small molecules through polymer matrices would allow for the rational selection of polymer materials used in these applications and their future optimal design. Although there has been reported an increasing number of studies on this subject over the last decades [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], the prediction of transport properties of gas molecules through glassy polymer membranes remains a difficult target. In many of the recent studies reporting molecular simulation prediction of diffusion and solubility of small gas molecules in several membrane models of the same glassy polymer a great scatter of the predicted values is observed.…”